


Invert & Pervert

by Nyarm



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, Alternate Universe - Underfell, Drunken Handjob, Dubious Consent, Ecto-Genitalia (Undertale), M/M, Tags added as they appear
Language: English
Status: In-Progress
Published: 2016-09-04
Updated: 2016-09-11
Packaged: 2018-08-13 00:55:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,394
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7955833
Author URL: https://archiveofourown.org/users/Nyarm/pseuds/Nyarm
Summary: <blockquote class="userstuff">
              <p>Sans finds himself transported to a strange place after a night spent fiddling with the machine in his workshop.  There's a Papyrus and Sans here, too, but...</p>
            </blockquote>





	1. Arrival

**Author's Note:**

> [Inspired by one of askellie's ideas hurk](https://askellie.tumblr.com/post/149737566826/plot-bunnies-up-for-adoption)

Sans blinked blearily as the harsh white of his surroundings came into focus.

“Ugh,” he groaned, rubbing furiously at his blurry eyesockets as he sat up. Where was he? The last thing he recalled was working on that stupid machine. He only went down to his workshop and worked on the machine to get a sort of refuge from Papyrus, who was being particularly bitchy that day. Apparently Undyne had kicked his ass while sparring and he decided that the best way to cope was to meet every minor infraction Sans made with a long, nagging lecture harp on every one of Sans’ faults. What a pain. That incessant nagging wasn’t new either, Papyrus complained about Sans’ habits and work ethic so often that he’d taken to calling his brother Boss to mock him.

He glanced around, wondering where the machine had dropped him off this time. On occasion, the machine would teleport him somewhere when he fiddled with it, but he never ended up too far from home. From the looks of it, he was somewhere in Snowdin Forest. He stood up and dusted himself off of the powdery snow. Some had ended up in his bones, but that would have to wait until he got home. It occurred to Sans that he would likely be greeted by his little brother with another scolding. He could just picture Boss yapping away about something or another. At least his baby brother was pretty cute when he had his face scrunched up in anger. Hah, even when he was irritating, Sans loved his Boss more than anything.

Sans started strolling past the dark fir trees with a smile, invigorated by his desire to get home and see his brother. Maybe he could even wrangle a hug out of the situation? His Boss was always especially happy to see Sans whenever he came home though he would fervently deny the fact if asked. Sans could always count on a forcefully hidden smile and a warm home-cooked meal to be waiting for him when he got returned. As Sans walked, though, he started to notice some… discrepancies in the area. Once he had broken through the treeline, he saw his sentry station looking unusually pristine and, instead of tempting mustard bottles sitting on the shelf, there were bottles of maple syrup? Strange, but it wasn’t unusual for the dogs to try to fuck with him by playing pranks. His hunch was confirmed by the fact that the run down lamp by his post had been swapped out for a similarly shaped chair. He shrugged and continued on, silently vowing to mess with Doggo later.

The snow crunched underfoot as he went on, easily bypassing his brother’s complex puzzles and all the other simpler, more overtly lethal traps set up by monsters hoping to catch Boss’ eye by emulating him. As if they could ever hope to be anything like his cool Boss, who was always intimidating and dangerous to everyone but Sans. By the time he made it to town, he was getting a little tired and was huffing lightly. That stupid machine, Sans thought, grumbling, how dare it drop him in the middle of bumfuck nowhere! He passed the Snowdin sign and started a brisk walk through town, shoving his hands in his jacket pocket and trying to look tough.

As he paraded, though, he noticed with surprise that the there were a strange amount of cat monsters lingering around instead of the usual horde of bunnies. Was there some kind of kitty litter convention today? He was annoyed, new people meant new threats. Usually, Boss was good about keeping the amount of new people at a safe, decidedly non-rebellious level. Sans walked a little faster, pulling up his hood and making sure to be extra conscious of his surroundings.

All the buildings looked the same, dreary and little deteriorated, the dark wood wet with snow. At least they did until he stopped in front of Grillby’s. He glanced at the sign, more than a little disturbed when he saw “Muffet’s” delicately spelled out in frilly pink cursive instead of Grillby’s plain, weathered sign. What the fuck. Did the spider queen get bored eating weary travelers in Hotland or… or was he somewhere he shouldn’t be? With a slow sort of creeping horror, it occurred to Sans that he might not be in his Snowdin at all. The syrup, the chair, the cats… was it possible the machine had teleported him to another universe? And, if this universe was different, then… then Boss might not exist. Sans panicked and bolted toward home, ignoring the fact that he looked an easy target, running as he was, through his sudden need to see if Papyrus was still there. Oh, god, he thought as the gravity of his realization sunk in, what if his brother wasn’t in this strange place at all?

He stopped in front of his house, breath coming out of him in short, harsh pants. It looked the same, at least. Same red fairy lights, same barred windows. He stumbled up to the front door while fishing for his keys in his pocket. Stepping into the house, he was met by the sight of a darkened living room, MTT - or NPT as the program stated- was playing on the TV, the bit of white noise a backdrop to this strange, scary situation. The light from the TV illuminated the table and couch in front of it, both far more polished than he remembered them being, he noted with some horror. The kitchen looked the same, but the table by the door had a vase on it instead of his pet rock. Shutting the door behind him, Sans went to go flick on the light switch, still apprehensive about what he might discover in this strange house, just barely different than his.

“M’Lord!” shouted a voice, and before Sans could react he was bowled over by some large monster. His face was buried in the monster’s coat and he immediately started to try and break free from the person’s strong grip. He flinched as the monster started rubbing and nuzzling all over him, who the fuck was this guy?!

“Get off me, freak!” Sans yelled, lashing out. He was such an idiot, letting his guard down like that - one of Boss’ many lectures echoed through his head and he was hit with another wave of panic. If this monster lived here, then where was his brother? The monster rolled off of him and sat on his haunches like some sort of dog. Sans scrambled up and glanced at the guy’s face before gaping in shock. It was Boss! Yet, he looked different. This Boss was wearing a hoodie like his own - black with a furred hood - and sweat pants with a single dark orange stripe going down the sides. His brother would never be caught dead wearing clothing like that! All Boss wore was skintight patent leather that showed far more than Sans would ever be comfortable with. This monster was openly giving Sans a lazy smile, too - another thing Papyrus would never, ever be seen doing. It was a strange sight, but… a nice one. His brother wasn’t too keen on letting his expressions stray from the strict guidelines of stoic, haughty, or grimacing. That didn’t matter now, though, and this wasn’t his brother.

“W-who are you?!” Sans cringed at his stutter, but he was just so weirded out! The Boss Look-A-Like looked at him strangely and was about to say something when the door was suddenly kicked in.

“PAPYRUS!” said the figure at the door who… who looked just like Sans?! What the fuck, this was just too much. This Other Sans was wearing enough leather for a BDSM convention and had a wicked scar over one of his eyes. Sans never thought he’d see the day where he was wearing tight black hot pants. Jesus.

“Huh? There are two,” Papyrus, Other Papyrus, Sans corrected, muttered. He looked confused but relaxed and gave a weirdly leering smile that reminded Sans of his brother. Even if this were a different universe, this guy was still Papyrus in some fashion, right? The leather clad Sans at the door had said as much. He was cut out of his reverie when the skeleton at the door cut in shrilly.

“WHAT KIND OF RAT DID YOU DRAG BACK HERE THIS TIME, TRASH? WHO ARE YOU?” asked the Other Sans, looking at him with disdain. He had his arms crossed and held himself like he was Queen of the Surface or some shit. This guy really didn’t recognize him? Sans realized that he had his hood up so he tugged it down and watched the uppity look on the Other Sans’ face dissolve into devious interest.

“OH?” He glanced over to Papyrus who smiled at him like he was sharing a private joke and slung an arm over Sans, who couldn’t help but relax into the hold, so much like his brother’s. Other Sans grinned at the interaction, “WELL. IT SEEMS LIKE YOU’VE ACTUALLY DONE SOMETHING CORRECTLY FOR ONCE. HE’LL MAKE A FINE PET!” Sans blinked at the guy’s words, appalled.

Pet?


	2. Oops

The Other Sans kicked the door shut with a resounding slam, as if to punctuate his adoption of Sans. Both the brothers were staring at him with freaky ass grins, but at least they didn’t seem too dangerous. They hadn’t tried to dust or attack him yet, and they were copies of he and his brother, so he let down his guard a little. He wasn’t quite sure what the guy meant, though. Did they plan on making him their maid or some shit? He didn’t really want to be delegated the position of servant. He hated work. Other Papyrus - who he figured he should just call Papyrus - still had his arm slung over Sans’ shoulders.

“Uh, I don’t really understand what you mean,” he stated awkwardly, trying to slip out from under the heavy arm holding him hostage.

“MEAN BY WHAT?” Other Sans asked, looking irritated at his lack of comprehension. That weird smile had dropped off into a pout and seeing such a petulant, baby-ish expression on his face was honestly creeping him out a little.

“Well, when you said-”

“OH! YOU REALLY DON’T KNOW WHAT YOUR DUTIES AS MY PET WILL BE?” Other Sans queried, loudly interrupting him. At least he got the point, Sans thought, slightly miffed. “WELL, I SUPPOSE I WOULD NOT MIND EASING YOU INTO IT. LET’S SET THE RECORD STRAIGHT, THEN.  FROM THIS POINT ON YOU WILL BE MY PROPERTY.”

“What.” Sans sincerely did not know how to even begin to approach whatever situation he’d found himself in. 

“YES, YOU MUST BE TAUGHT SOME RULES, THOUGH. HMM, I OUGHT TO BE GOING TO ALPHYS’, BUT, PERHAPS…” Other Sans trailed off, his harsh, jagged eyelights snapping towards Papyrus. “MUTT, TEACH HIM THE ROPES WHILE I’M GONE.”

“Of course,” Papyrus answered, sounding for all the world like a respectful, obedient servant. He still had that lazy, serene look on his face that looked all at once alien and comforting on his brother’s face. Sans was fairly certain he was going to end up a maid at this point.

“GOOD,” Other Sans said sharply, before passing them by and trekking deeper into the house, presumably to fetch something. Sans glanced toward Papyrus, who’d made his way over to the couch and was beckoning for Sans to follow. He got up and went to him, being careful to sidestep a wire that ran under the television.

“So, what should I expect to be doing here?” Sans asked, figuring he may as well try to assess the situation. It suddenly occurred to Sans that he would have to attempt to make his way back to his own universe at some point. He felt a bit of anxiety rise up in him at that and breathed out to steady himself. One step at a time, just like Boss had always said.

“Don’t worry about it,” answered the weirdly relaxed Papyrus, hands tucked away into his hoodie as he slouched further into the couch.

Sans was a little irritated by the dismissive answer. “Didn’t he tell you to teach me some stuff?”

“I guess I did.” He shrugged, chuckling a little. Sans couldn’t help but think of how long it’d been since he’d heard his brother laugh that openly. “Are you really that invested? We could just hang out for a while, instead,” Papyrus said. A scant few seconds after he spoke, Other Sans stomped down the stairs and out of the house with a dismissive wave. 

“M’lord is so hasty,” Papyrus commented as he reached for the remote lying uselessly on the table.

“Why do you call him that?” Sans asked, honestly curious. Since it seemed that this was some alternate universe, it was likely that the nickname had similar roots to Boss’. Speaking of which, he'd noticed that the power in this household seemed to be swapped somehow. Other Sans was a bossy little guy, whereas Papyrus was very passive. 

“Hm? Because he is my lord, my master, my owner,” Papyrus stated with a strangely intense look on his face. Okay, then. Sans felt pretty sure at this point that they had a weird ass relationship.

“Actually, that’s probably a rule. I think? It’d please him if you called him your lord, so do that,” Papyrus advised. Hah, there was no way Sans was going to call him something as stupid as that. Maybe he’d just call him Blackie, like a little blackberry, which was uncreative, but the guy wore a shit ton of black and that pout earlier hadn’t led Sans to believe he wasn’t the toughest guy around. It was good enough for now, he supposed. Papyrus spoke up again, “By the way, what’s your name? I’m going to hazard a guess and say it’s Sans, but…”

“Um, it’s Sans,” He answered. Papyrus nodded, clearly unsurprised, and changed the television channel. It was a show starring some robot named Napstaton? He looked a lot like Mettaton, so Sans chalked it up to more alternate universe bullshit. Sans glanced over at Papyrus, taking the momentary lull in conversation to really look him over. He really did look the same as Boss. He had the same long limbs, handsome, angular face, and sharp bone structure, but he was different somehow. Even if Sans ignored his casual clothing, he couldn’t look past his relaxed posture and serene face. It was strange because he never saw Boss like that, but nice because he  _ never _ saw Boss like that. The gratuitous screaming and squelching from the television played the part of disconcerting white noise. 

“You want something to drink?” Papyrus asked, getting up. Sans nodded and watched as he made his his way to the kitchen. While he was gone, Sans gave his surroundings a cursory glance. The house was pretty much an exact replica of his and Boss’ which was good because it at least meant that he knew where all the exits were, if things went south. Papyrus strolled out from the kitchen with a decently sized jug in tow. Sans had no idea where he got fucking moonshine from, but okay.

Papyrus plopped the drink onto the coffee table, “Muffet’s special brew, a favorite of mine.” He poured some into a couple of mugs and pressed one into Sans’ hands before sitting back down, somewhat closer than before. Muffet? Sans didn’t know she made alcohol, though it seemed like she had taken Grillby’s place in this world. He thought to the pretty sign he’d passed earlier and sighed. He couldn’t really imagine her slinging burgers.

Sans took a tiny sip and winced a little because, fuck, that was strong as hell. He could hear Papyrus laugh at him and take a long, pointed gulp of the brew without so much as flinching. He glared at him, feeling a warm, red flush rise to his cheekbones as a result of his embarrassment. Was that supposed to be a god damn challenge? He would more than rise to the occasion, Sans thought, knitting his eye ridges together with a determined expression. He knocked back the rest of the cup to show off, but ended up coughing at the burn as it hit his magic. Papyrus scooted over to pat him on the back and Sans felt himself blush again.

He and Boss had always spent sometime curled up against each other on the couch after a long day of work, so Sans felt himself leaning into Papyrus, who’d taken to tracing his phalanges up and down his back, reveling in the familiarity of the touch. He realized that he probably shouldn’t have downed that mug so quickly. Sans was small and admittedly a lightweight, so when he felt a drunken buzz settle over him, he really shouldn’t have been surprised. Papyrus refilled his drink and they drank in silence for a while, refocusing their attention on the terrible show playing on the television. It seemed to have switched to footage of a loud dance club? Though the cameras were mainly focusing on the robot DJ and his terrible wubs. They stayed like that for a time, a little drunk and Sans found himself half way into Papyrus’ lap before he spoke up, “You know, you look exactly like my brother.”

“Really? You look exactly like mine. How surprising.” Papyrus shifted to stare down at him, amused, eyelights a little fuzzy. “You seem a little less frigid, though.” He glanced upward, as if considering something before speaking again, “Hm, there’s a thought.” He slipped his eyes closed before dropping a hand to thumb at Sans’ waistband, intentions clear as day. Sans started a little, but, fuck, maybe it was the alcohol that had him feeling like this was great idea. This guy was basically a chiller Boss, right? Things were kinda hazy right then, so Sans just leaned into his touch. Papyrus slipped his hand into Sans’ pants, rubbing from the iliac crests down to the sensitive edges of his pelvic inlet.

“Mmm,” Sans moaned, slumping into the taller skeleton’s shoulder as skilled fingers stimulated him in all his favorite spots. He could feel tingling waves of warmth gathering in his pelvis and knew he was ready to form something. But what? This day had been pretty shitty, he felt like he’d gotten shafted by the multiverse pretty hard. A dick day. He tugged down his pants to let his freshly formed cock spring free. Papyrus placed a single phalange on it, rubbing at the slit on the head and making Sans writhe at the jolt of pleasure shooting through his cock. Sans felt his large hand wrap around his cock and stroke up and down, run-off magic doing a fine job of lubricating it’s delightful passage. Sans felt his bones tense and warm at the sensation, Papyrus’ firm grip constricting him in ways he could never do to himself. Sans leant back and whined, bucking his hips into the touch. It was so good and everything was hazy and slow and that made it feel better. Boss was smiling at him and wasn’t that great? How rare. Sans reached up to try to reciprocate, hands shaky at the wonderful feelings coursing through his marrow, but had his hands batted away. He felt like he was going to cum. That was pretty sad, but he was drunk and pleasured and Boss had never minded an early shot right? 

“H-hah,” Sans gasped, tears pricking at the edges of his eye sockets as he came into that tight, hard grip. He rutted into it desperately, spurts of red cum painting Boss’- wait. Not Boss. Shit. _Shit._ _Not Boss._ In a sudden moment of sobriety Sans remembered that he was not home, this was not his brother, and what he just did was tantamount to cheating, even if he used the flimsy excuse that they were the same person. Sans felt like shit. He was shit.

“Did you cum hard enough to become mute?” Papyrus laughed at him, wiping jizz on his sweatpants. Sans gave him a weak smile, not sure what to say, still swimming in guilt because  _ god _ what had he done? Being drunk was no excuse.   

What a mess.

**Notes for the Chapter:**

> rip uf sans
> 
>  
> 
> pixie-pier.tumblr.com


End file.
